1. Field of the Invention
This invention relates to a process of vapor phase catalytic hydrogenation of maleic anhydride to gamma-butyrolactone, and, more particularly to such process which is carried out using an activated catalyst, and under predetermined reaction conditions, which enables a substantially quantitative conversion and high selectivity to gamma-butyrolactone during a prolonged period of production.
2. Description of the Prior Art
Vapor phase catalytic hydrogenation of maleic anhydride to gamma-butyrolactone (hereinafter referred to as "butyrolactone") is an old and well established art for which a great many processes and conditions have been tried. However, commercial practice in respect to the production of butyrolactone from maleic anhydride has not been entirely successful, especially in terms of high conversion and high selectivity to butyrolactone. These deficiencies usually occur because of low catalytic activity and/or less than optimum process conditions.
Dunlop, in U.S. Pat. No. 3,065,243, for example, described a process in which a feed compound, such as maleic anhydride, succinic anhydride, or an acid or ester thereof, was vaporized and the vapors in hydrogen passed over a reduced copper-chromite catalyst. However, conversion and selectivity to butyrolactone was relatively low.
Kyowa, in U.K. Patent No. 1,168,220 disclosed that a reduced copper-zinc catalyst could be used in place of copper-chromite but with only marginally improved results.
Miller, in U.S. Pat. No. 4,001,282, described a similar vapor process carried out in the presence of water. The catalysts used were reduced copper-chromite, copper-zinc, and copper-zinc-chrome catalysts. Water, however, increased the complexity of the process and, accordingly, the process did not attain commercial success.
De Thomas, in U.S. Pat. No. 4,105,674, used relatively expensive copper-palladium or copper-platinum catalysts to carry out the hydrogenation.
Miya, in U.S. Pat. No. 3,580,930, utilized a copper-zinc-chromium catalyst in an attempt to minimize the formation of by-products. Low yields of butyrolactone were obtained, however, with this catalyst.
Attig, in EPA 332,140, published Jun. 28, 1989, described vapor phase hydrogenation of maleic anhydride to tetrahydrofuran and butyrolactone using a catalyst comprising copper-zinc-chromium-alumina. Selectivity to butyrolactone, however, was only 50% or less.
In commercial operation according to these and other processes, however, the catalysts and process conditions employed have been found to be less than satisfactory, usually because the catalyst was deactivated through tar and coke formation within a relatively short time. The short life of these catalysts has made it virtually impossible to carry on a production run for a prolonged period of time. The catalysts inevitably had to be regenerated, if at all possible, within a very short period, and fresh catalyst soon introduced into the system. Such procedures required time-consuming shut down times which increased the overall cost of the process.
Accordingly, it is an object of the present invention to provide a process for effecting vapor phase catalytic hydrogenation of maleic anhydride to butyrolactone in high conversion and selectivity during a prolonged production run without requiring fresh catalyst to be introduced into the system.
Another object herein is to provide such a vapor process which provides butyrolactone in a conversion of feed material of 95% or more, preferably 100%, and in a selectivity of 80% or more, preferably 90-95%, or more, during production runs of at least about 2000 hours.
Another object of this invention is to provide an activated catalyst for achieving substantially quantitative conversion and high selectivity to butyrolactone.
Still another object of this invention is to provide such a process which employs an activated catalyst therefor, and process conditions for carrying out the hydrogenation effectively, including a defined ratio of hydrogen to feed compound in the vapor mixture, a predetermined contact time, and a selected feed rate, under which conditions high conversion and selectivity of maleic anhydride to butyrolactone can be achieved by a vapor process.